The three of us were in the street at the front of a friends house working on a car engine at about 2PM. Two of us had our heads under the hood and were busy when the third person told us to look up at the plane. The weather was clear blue sky. The plane looked like a Boeing 747 or larger and was travelling from East to West at a height of between about 1500 and 2000 feet, or about 4 hand spans at arms length. The plane produced a contrail (chemtrail?) from the trailing edges of all wing and tail components. There were no engine pods observable on the aircraft anywhere, there was no noise at all. There were no beacon light flashing on the aircraft?. If you look at a map of Hobart the plane was flying over the top of the city and most of the suburbs of the city. It was coloured dark grey (battleship grey?). There were a large number of ribs running under the wings (in parallel with the fuselage. The plane was free of any identifying nember or letters that I could see.